PROTEOMICS OF DIFFERENT CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS

S. aureus causes severe infection even if it is mainly a harmless bacterium. It exists in a oxacillin-resistant (meticillin-resistant S. aureus, MRSA) form that represents the most important cause of antibiotic-resistant healthcare-associated infections worldwide. Most MRSA strains contain Panton-Valentine leukocidin (PVL) genes, that encode for a citotoxin that is one of the essential components of the virulence mechanisms of S. aureus. Furthermore, the presence of PVL is also associated with increased virulence of certain strains (isolates) of S. aureus. Although clinicians are currently concerned primarily with MRSA infections, methicillin-susceptible S. aureus (MSSA) infections can be present with similar epidemiologic and clinical characteristics when are PVL positive. In this study, 2-DE coupled with mass spectrometry has been used to compare protein profiles of (PVL+) and (PVL-) MRSA and MSSA S. aureus in order to highlight protein differences related to PVL presence or absence. Bacterial samples were isolated from human infections and classified on the basis of PCR analysis and antibiotic susceptibility test. Quantitative two dimensional electrophoresis was performed on MSSA and MRSA samples further classified in PVL+ and PVL-. Experiments were done in triplicate using custom IPG strips pH 4-5.5 to optimize spot resolution and to visualize different isoforms on gels. Image and statistical analysis were performed with Progenesis SameSpots software (Nonlinear Dynamics), proteins differentially expressed (ANOVA p<0.05) were identified by MALDI-TOF-TOF for identification. 2-DE image analysis revealed the differential expression of several proteins involved in iron metabolism and oxidative stress.